The objective of this paper is to present some results of laboratory experiments during the investigation of stress-strain characteristics of Carboniferous sandstones at dynamic loading. During these experiments increasing frequency and the constant amplitude of dynamic loading and/or constant frequency at different amplitude of dynamic loading were applied.

Der Gegenstand dieses Artikels ist, irgendeine von Ergebnissen von Laborexperimenten bei Messung der Spannungs- und Deformationscharakteristik der Karbonsandsteine bei ihrer dynamischen Belastung vorzustellen. Im Laufe diesen Experimenten wurden entweder anwachsende Frequenzen bei konstanter Amplitude der dynamischen Belastung, oder gleiche Frequenzen bei variabler Amplitude der dynamischen Belastung verwendet.

L'objectif de ce papier est presenter quelques resultats d'experiences de laboratoire pendant l'enquête de caracteristiques de la tension - deformation de grès Carbonifère à sollicitation dynamique. Pendant ces experiences frequence croissante et l'amplitude constante de sollicitation dynamique et/ou frequence de la constante à amplitude differente de sollicitation dynamique ont ete appliquees.

Introduction

At Czech hard coal underground mines, the highest safety risk represents anomalous geomechanical events, especially rock bursts. Understanding of the dynamic behaviour of the rock mass, which surrounds coalface during seismic event, is very important for justifying of rock burst damage. For this reason, problems of the genesis of developing rock bursts, their influencing factors are under settlement. The research of strength and strain characteristics of rocks under dynamic loading is aimed at evaluating these characteristics to identify better the behaviour of rocks during anomalous geomechanical events, mainly at rock bursts.

In the laboratory mechanical properties of rocks were studied on MTS equipment, which is a system enabling the static as well as dynamic loading of rock specimens. From the point of view of applications of measurement results, parameters of dynamic loading similar to those observed during seismic events in the rock mass should be used in the laboratory to recognize rock behaviour at anomalous geomechanical events

This paper describes the rock characteristics mainly during dynamic uniaxial compressive loading depending upon the frequency and amplitude of dynamic loading.

Parameters of seismic waves during rock bursts

For laboratory investigation of rock samples under the dynamic loading, which should contribute to better understanding of rock burst phenomena manifestation, the best way is that frequency of laboratory dynamic loading will be the same and/or similar at least as during rock burst.

For estimation of prevailing frequencies during rock bursts occurring in the Ostrava-Karvina coalfield within last ten years, the frequencies of P wave maximum were investigated. Results of detailed analysis are presented in the graph as a dependence of released seismic energy of rock bursts versus prevailing frequency of P wave maximum (see Figure1).

(Figure in full paper)

In this graph rock burst energy has logarithmic scale and it is visible, that the strongest rock bursts have frequency of P waves of about 5 Hz. Therefore laboratory investigation of rock samples under dynamic loading was estimated in the range of frequencies 0–10 Hz.

The evaluation of rock behaviour under dynamic loading

The mechanical rock characteristic affects, to a considerable extent.

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